


The Ultimate Rule

by scarletmanuka



Category: Marvel Cinematic Universe, Stargate Atlantis
Genre: Crossovers & Fandom Fusions, Established Relationship, M/M, Peter and Tony are on a Stargate team, Relationship Reveal, wraith attack
Language: English
Status: Completed
Published: 2019-12-09
Updated: 2019-12-09
Packaged: 2021-02-25 05:22:31
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,028
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21730768
Author URL: https://archiveofourown.org/users/scarletmanuka/pseuds/scarletmanuka
Summary: Peter, Tony, and their gate team have transferred to Atlantis. For their first mission, they will join AR1 on a simple visit to an established trade partner. Of course, nothing ever quite goes to plan...
Relationships: Peter Parker/Tony Stark, Rodney McKay/John Sheppard
Comments: 15
Kudos: 39





	The Ultimate Rule

**Author's Note:**

> Based on a moodboard by [a href=https://starker-sorbet.tumblr.com/post/189179214697/starker-stargate-au-where-tony-is-a-sg-team-leader]starker-sorbet on Tumblr[/a], I figured I'd have a go at writing a Starker/McShep crossover.

Peter bounced on the balls of his feet as he waited patiently in the Gate Room for Tony and Sheppard to finish talking with Elizabeth Weir so his team could go on their first ever mission in Pegasus. He craned his head backwards and looked up, still unable to get used to the sight of the Ancient city. He was finally in _Atlantis_ , and it was all that he’d ever dreamed it would be. He was one of the youngest scientists to ever be recruited by the Stargate program and as soon as he’d learned of the lost city of the Ancients, he’d wanted to come. He’d only just joined when the expedition first set off to Pegasus and so his request had been denied and he’d spent the past year on SG9 instead. 

Which he really wouldn’t trade for the world.

He’d been orphaned at a young age and taken in by his aunt and uncle, but Ben had died in a mugging-gone-wrong several years ago and only a year later, May was killed in a hit and run. Peter had been left tetherless and alone, which was why he’d not hesitated when Colonel Carter approached him at University one day and had him sign an NDA before telling him about an opportunity that she had for him. He had nothing holding him back and he desperately needed something to distract him from his grief. He’d then met his new team and discovered that a family forged in fire were just as strong, if not more so, than a family of blood ties. 

Major Tony Stark, their team lead, was highly intelligent, funny, and charming. He’d talked their way out of many a situation, avoiding bloodshed, but didn't hesitate to do whatever was needed when the time called for it. Sergeant James ‘Bucky’ Barnes was the team’s second; trained in special ops and a crack shot, he’d saved Peter’s ass on more than one occasion. In keeping with the SGC tradition of having aliens as team members, Carol Danvers was the remaining team member. She came from a planet called Hala, which had been under the influence of the Goa’uld System Lord, Yon-Rogg, and she had quickly become Peter’s best friend.

Peter’s attention was drawn back to the discussion close by when he heard his name mentioned but it was simply Sheppard explaining that he’d be with McKay, tracking down the unusual energy reading. Tony looked up and saw Peter watching and his lips curled up slightly in a private smile, and Peter looked away before his blush would give him away. There had always been a sexual tension between Tony and himself which had turned into more when they had spent two weeks stuck in a damp prison cell together on P85-901. Since then, they’d been careful to be discreet, lest Tony be dishonourably discharged but with Bucky and Carol’s support, they’d managed to avoid giving their relationship away. They’d snagged quarters next to each other when they’d arrived in Atlantis and they’d spent their first night making love on Tony’s balcony, the sound of the ocean in their ears and the light of a different galaxy softening their features. Peter hadn’t thought it could get any better but then Tony had pulled him close and whispered, “I love you,” into his ear and it was then then Peter knew that he never wanted to leave Pegasus.

“Alright, listen up,” Sheppard announced as he and Tony walked over to join the rest of their teams. “We’re good to go, but be on your guard. There’s no such thing as a milk run in Pegasus and things can and will go to shit in an instant. Barnes and Danvers, you’ll be with Teyla and Ronon, meeting with the local Chieftain to discuss the continuation of our trade agreement. Stark and I will be watching our geek’s backs as they investigate the power reading in the ruins. With any luck we’ll be in and out in six or so hours and be back in time for dinner.”

“And it’s roast beast tonight so we do _not_ want to miss that,” McKay piped up, rubbing his hands together.

“Roast _beast_?” Bucky asked warily.

“Kind of a cross between beef and venison,” McKay explained. “It’s quite good.”

Bucky pursed his lips at this and nodded. “Sounds it.”

Carol smacked him on the stomach with the back of her hand. “That’s our Buck, always thinking with his stomach.”

Bucky looked down at his rock hard abs, hidden behind his tac vest. “I’ll have you know that this is a delightful stomach, Danvers.”

She winked. “Yeah, yeah, you’re the envy of everyone. Except for Teyla - I think her abs are harder than yours.”

“Oh yeah, without a doubt,” he said and grinned at the Athosian.

“Pfft, no one has better abs than Teyla,” McKay snorted. “It’s not even a competition.”

 _“Focus, people,"_ Sheppard drawled and despite the laidback tone, everyone instantly became more serious. He might appear too casual to be a commander, but Sheppard had the respect of everyone on Atlantis and Tony had been eager to work with him. When they’d found out what he’d done to keep the expedition alive in the first year that they’d been on Atlantis, Peter’s team were awed. The brass might not have been fans of Sheppard’s, but everyone else was and tales of how he’d taken out an entire Genii strikeforce single-handedly had spread throughout Stargate Command like wildfire. Theirs was a culture that embraced ‘leave no man behind’ and Sheppard embodied that as much as Jack O’Neill did. There had been no shortage of volunteers for teams to work under Sheppard - former SG9 included. 

“Dial her up, Chuck,” Sheppard instructed and Peter watched as the gate dialled, so different to the ones in the Milky Way. The wormhole blossomed out from the gate and then settled back to pool in an ethereal blue glow. Ronon, Telya, Bucky, and Carol led the way, followed by McKay and Peter, with their team leads bringing up the rear. Peter blinked at the bright light as he stepped out onto Tahnar, his hand resting lightly on his Beretta, his eyes taking in everything. The teams fanned out around the gate, checking for danger and soon Sheppard was giving the all clear. They headed down the well-worn path leading away from the gate and when the path split into two, Peter headed one way with McKay, Tony, and Sheppard while the others continued on into town.

“I want radio check ins every half hour,” Sheppard instructed. “Give Altain my regards.”

“What about Lein? Do you send her your regards also?” Teyla asked, her lips twitching into a smile.

Sheppard looked pained. “Sure, of course, give Lein my regards as well.”

Ronon barked out a laugh and Peter turned to McKay to find out what was so funny only to find an unhappy frown on the man’s face. “Who’s Lein?” he asked.

“Altain’s daughter,” McKay said glumly. “Wherever we go, women throw themselves at Sheppard. There’s not a planet we’ve been to that doesn’t have a chieftain’s daughter, or a priestess, or a councilwoman pining over him.” He glanced over at Tony. “Same thing’ll happen with Stark, mark my words. There’s something about pretty flyboys that makes the women of Pegasus drop their panties the second they see them.”

Peter couldn’t tell if it was jealousy of the Colonel’s ability to attract women or jealousy for another reason that was making McKay so unhappy but either way, he couldn’t mention that he had no reason to feel jealous himself. Women could throw themselves at Tony all they wanted but it wouldn’t do them any good. Peter knew that Tony loved him and he wasn’t going to look twice at a drooling priestess. 

It was a several click walk to the ruins where Sheppard’s team had picked up a strange energy reading the last time that they’d visited but it was a pleasant day and the walk was enjoyable. Shappard and Tony spent the time chatting about the different planes and choppers that they’d flown over the years, but they remained on alert, eyes scanning constantly. Peter tried to be just as wary, keeping the Colonel’s warning in mind, but McKay started talking about what the readings could possibly mean and before he knew it, Peter was completely distracted by their conversation. They both grew animated as they spoke, and Peter soaked up every scrap of knowledge that he could from McKay. He’d always hoped that he’d get the chance to work with the brilliant scientist and he wasn’t at all disappointed. Peter had never met anyone who had so much knowledge about so many things. He’d been warned by Bill Lee and a few of the other scientists at the SGC about McKay, that he was petty and arrogant and caustic, but Peter didn’t find him that way at all. Arrogant? Maybe a little, but was it really arrogance when you could back up your claims? 

They reached the ruins and Peter looked up, amazed that they’d arrived already. Tony rolled his eyes at him and bumped his shoulder fondly as he passed by. “Good thing you got me watching your back, sport,” he murmured and Peter felt himself blushing. He knew better than to get distracted while off world and he’d gone and done exactly that. Neither Tony nor Sheppard seemed overly upset about it however. In fact, from the faintly amused gaze that Sheppard was giving McKay, it seemed that this was a regular occurrence for their team as well. It made sense now why Sheppard had divided their teams up so, with the team leads protecting the scientists. It wasn’t because he’d wanted to avoid the negotiations, but because he knew that McKay and Peter would need to be kept supervised.

“Okay, McKay, you and Wonder Kid are up,” Sheppard said. “Do your thing.”

“My ‘thing’?” McKay asked just as Peter said, “Wonder Kid?”

“Yeah, McKay, your thing, where you make some crazy scientific discovery that will probably one day save our asses.” McKay seemed to be placated by this somewhat but Peter was still glaring at the Colonel. Who simply smirked at him. “Looks like Boy Genius takes after you, McKay. Looks like he could be a firecracker.”

“This firecracker has a name, you know,” Peter growled.

Sheppard smirked again and Tony chuckled and Peter just rolled his eyes and turned to McKay. “Shall we?”

“Yes, let’s get to work,” McKay agreed. “We’ll leave these two to communicate in a series of clicks and grunts like the cavemen that they are.”

“Oi!” Sheppard protested, but Peter could tell he wasn’t serious. It seemed that teasing the scientist was a regular past time for him and the fact that he was including Peter in that made him feel rather welcome. Tony winked and then grunted at Sheppard and the two wandered off to cover the exit.

An hour later, the innards of an Ancient console lay scattered across the floor and Peter and McKay were on their backs, half inside the console, looking up at the crystals above them. “This is the strangest energy reading I’ve ever seen,” Peter admitted, turning his head to check the scanner once more. “Have you seen anything like it?”

McKay frowned. “No, which is odd. I’m beginning to think that we might not be dealing with an entirely Ancient technology.”

“Really? You think someone’s cannibalised it?”

He hummed thoughtfully. “Something like that. Let me swap these crystals out and see if that makes a difference.”

Peter nodded and reached out to pick up the crystal they needed just as their radios crackled to life. There was static and then faintly they could hear Teyla’s voice but they couldn’t make out what she was saying.

“Teyla, please repeat, you’re breaking up,” Sheppard said.

Peter and McKay paused, watching Sheppard, as Tony swept his gaze around the chamber. 

There was another burst of static and what could have been the sounds of gunfire.

“Teyla, report!” Sheppard barked but got no response. He tapped his earpiece again. “Ronon, do you copy?” Silence. “Barnes, Danvers? Does anyone copy, over?”

“What do you think is going on?” Peter whispered to McKay.

“Nothing good from the sounds of it,” he replied, his eyes never leaving Sheppard.

Several minutes passed as the Colonel continued to attempt to hail their teams and both Peter and McKay pulled themselves out from under the console to sit on the floor, waiting warily. “Alright, let’s pack it up,” Sheppard said, waving a finger in a circle. “We’re gonna have to check out what’s going on.”

“Is it really necessary for Parker and I to go?” McKay asked. “We’re close to figuring this out.”

“Yes, McKay, it is,” Sheppard said firmly. 

“But, we could -”

“Rodney,” the Colonel repeated, drawing out his name until it had several more syllables than usual, “pack it up.”

“I just don’t see -”

_“Now.”_

McKay huffed and then began gathering tools and spare parts into his backpack. Peter exchanged a worried glance with Tony and then did the same, eager to see if his teammates were okay. There was another squawk of static from their radios and then Teyla’s voice. _“Colonel Sheppard, Wraith!”_

“Fuck,” the Colonel swore but before anyone could do anything else, Tony was suddenly thrown across the room, crashing painfully against the opposite wall. Sheppard got off a short burst of fire from his P-90 but then he too was flung aside. Peter saw a tall, hulking figure with long white hair stalking towards him and he scrambled backwards on his butt, having not gotten off the ground as yet. He got his gun out of its holster and fired off three shots before it was plucked from his grasp and discarded. The Wraith growled down at him, and reached back with one arm, his hand held open to feed.

“Eat this!” McKay cried and emptied his own gun into the Wraith, causing its body to jerk as he emptied his clip into it. The Wraith didn’t seem at all perturbed, simply threw out an arm and swiped McKay away as easily as one would brush away a fly. The hungry gaze was soon back on Peter and he tried to get away but he was backed up against the console and he had no room to maneuver. The Wraith pinned him down with one booted foot and then snarled as he drew his hand back once more. 

“Peter!” he heard Tony cry out and then his lover was launching himself at the Wraith’s back, he arms slipping around its throat to try and choke it, his knees pinning in tight to its ribs. 

Peter grabbed the closest thing he could find to use as a weapon - the crystal they’d been going to replace - and he shoved himself upwards, swinging the crystal in his grip. The Wraith was much taller than him but he managed to connect soldily with the side of its face and it immediately turned its attention back to him. Tony pulled out his own sidearm and levelled it against the Wraith’s neck, pulling the trigger, and yet it still didn’t stop it. The crystal had dropped to the ground, shattering, and Peter stooped to pick up a shard and he plunged it into the Wraith’s chest. The creature was unstoppable and one of its fists flew out, connecting with the side of Peter’s head, sending him sprawling on the ground. With one of its attackers disabled, it reached back and pulled Tony off its back, pulling him around to the front by his throat, a snarl on its blood smeared lips. “I’m going to enjoy feeding on you, human,” it rasped.

“Hey asshole, don’t play with your food before you eat it,” Sheppard called out and as the Wraith turned at the sound of his voice, he opened fire with his P-90 and filled it with bullets.

The relentless fire finally did the job and the Wraith collapsed, dropping Tony as it died. Peter crawled across the floor to Tony, clutching at his face as he got there, checking to ensure that he was breathing. “Tony?” he whimpered, patting at his cheek, willing him to open his eyes. “Tony, can you hear me?”

Tony groaned and his eyes finally fluttered open. “Hey, babe, ‘m here,” he rasped.

“Oh thank fuck,” he gasped and slumped down into Tony’s arms, pressing a quick kiss to his lips. “Holy shit, that thing just didn't stop. I thought I’d lost you.”

“Mmm,” his lover agreed. “Bit different to seeing it in person, huh?”

“It must have fed recently,” McKay told them and Peter looked up to see him watching them. “They’re resilient to our weapons but not usually _that_ resilient.”

“Come on, we need to find the others,” Sheppard said and Peter froze, suddenly realising the position he and Tony were in and knowing that they’d just outed themselves to Tony’s commanding officer.

McKay helped Peter get Tony to his feet and they limped from the ruins, Sheppard leading the way, his P-90 held steady in front of him. Down the path leading to the village they spotted four figures and soon they could make out their teammates. 

“Colonel, are you alright?” Teyla called as they came running up.

“Yeah, we’re pretty much in one piece. What happened?”

“Single dart came through the gate,” Ronon explained. “I managed to shoot it down but by the time we got to it, the Wraith was gone. Tracks led this way and we came as soon as we could.”

“There haven’t been others come through after it?” Sheppard clarified.

“No, not that we’ve witnessed,” Teyla answered.

“Hey, boss, you okay?” Bucky asked Tony, worried eyes lingering on the bruising on his throat.

“I’m good,” he promised in a hoarse voice. “Petey will need to be checked over for a concussion though.”

“All three of you will need to see Carson,” Sheppard told him, gesturing at them and including McKay.

“I think we’ll _all_ be visiting his voodoo practise,” McKay said. “Don’t think I didn’t see you getting up close and personal with that wall, Colonel.”

Sheppard narrowed his eyes. “I’m fine, Rodney.”

“Why don’t we let Carson be the judge of that?”

He huffed out a breath. “Fine. Let’s head back to the Gate.”

As they made their way back down the path, Peter allowed the others to gain a little distance until he and Tony were out of earshot. “I think the Colonel knows,” he whispered. “About us.”

Tony met his gaze and his expression was grim. “I know.”

“What are we going to do?”

“Not much we can do, baby.”

“But they might send you home!”

Tony reached out and gave Peter's hand a quick squeeze. “We’ll deal with that if and when it happens, okay. Don’t go borrowing trouble.”

Peter couldn’t help fretting though and he went through the post-mission check up in the infirmary and the debrief with Weir in a daze. Sheppard barely glanced at Peter the whole time and he wondered if the Colonel blamed him for bringing about the ruination of one of his majors. By the time they were dismissed, Peter was trembling all over and jumping at every noise and couldn’t concentrate on anything. He went back to his room and showered, then sat in the dark on his bed, staring at the wall. When his radio crackled to life and Sheppard requested that Tony and Peter meet him in the gym, he couldn’t help the pained moan that fell from his lips. This was it. Sheppard obviously respected Tony enough that he hadn't raised it in front of Weir, but was instead waiting to get them somewhere private before giving them their marching orders.

Peter was the first of himself and Tony to reach the gym and he nodded towards Sheppard and McKay but said nothing as he took a seat on one of the wooden benches. Tony arrived shortly afterwards and he sat next to Peter, their arms brushing against one another and their legs pressed close together. It was selfish of him, but he didn't move away to detract attention from their relationship, instead he memorised the feeling of what it was like to be so close, worried that he'd soon lose it.

“I’ll just get the door,” Sheppard said, indicating that no one else would be joining them, and soon the door to the gym was closed and locked. Once he was assured of their privacy, he turned back to the two newcomers. “So, today was a clusterfuck but not the worst thing that you’ll encounter here in Pegasus. Having said that, you both handled yourselves well so congratulations. There is however something that we need to discuss.” His tone was light and casual but Peter felt himself flinching from it nonetheless. “There’s one rule above them all that we abide by here on Atlantis and those who can’t follow it find that they don’t last long here. We’re a close knit community and trust is more important here than on any other assignment that you’ve ever had. If we can’t trust each other, then someone’s gonna end up getting someone killed, it’s as simple as that.”

“Stop beating around the bush, John,” McKay snapped and Peter’s head swung about in shock to look at him. He wasn’t American military so it seemed odd that he’d be chiming in on the conversation.

“They need to be aware of the importance, Rodney,” Sheppard said easily.

“From what I can tell, they already are,” McKay said, giving Peter a knowing look.

“So what’s the rule?” Tony asked, his eyes sharp as he watched the two Lanteans.

“It’s simple,” Sheppard said as is gaze fell back on them. “You do everything it takes to take care of your scientist. You protect him with everything you got. Everything.” His face suddenly lit up as he smiled at them. “Looks like you’ve got it in hand already, but you let me know if you have any trouble with any of the other newbies around here. We don’t tolerate anyone who doesn't follow the rule.”

Peter felt his mouth dropping open in shock but he couldn’t help it. “But, don’t the other rules override that one?” he asked.

“Nope,” Sheppard assured him. “That’s the ultimate rule and anyone who doesn’t follow it finds themselves Earth bound before long. Now, Stark, I recommend you take some time tonight to take care of your geek - it’s been a rough day. He might need a bit of extra care today.”

McKay snorted. “Why not just tell them to fuck already.”

Peter choked on his own spit and sat coughing for a long minute as Tony thumped him on the back. Had he really just heard that?

“And how will _you_ be taking care of _your_ geek tonight?” Tony asked the Colonel archly.

Sheppard winked. “Same as you, I imagine.”

“Huh,” Peter said.

McKay rolled his eyes and then stood up. “Now that you’ve finished torturing them, can we please get on with it? There’s a lot I want you to do to me tonight, John, and the clock is ticking.”

Sheppard smirked and got to his feet. “Sounds like I’ve got my marching orders. Enjoy your evening, gentlemen.” And then he was off, following McKay from the room and leaving Peter alone with Tony.

“Did that actually just happen or did I hit my head harder than I thought?” Peter finally asked.

Tony was grinning and he stood up and held a hand out for Peter to take. “No, it really did just happen.” He took a lusty breath and let it out. “I think I’m going to like it here.” He tugged on Peter’s hand and set them in motion towards the door. “Come on then, baby - we’ve got a rule to uphold.”

Peter allowed himself to be led to the door, and as they let their hands drop apart as they made their way into the corridor he found himself agreeing that he was really going to like it here too.


End file.
